Dissolution rate of apatite powders in acidic fluoride solutions and the relationship to hydroxyapatite disk and bovine enamel behavior

The dissolution kinetics of synthetic hydroxyapatite (HAP) and carbonate-containing HAP powders have been studied in fluoride-containing acetate buffer solutions partially saturated with respect to HAP (K,, = 10-‘15 to IO-“‘). The experimental results indicate that in the ease of HAP powders the dissolution rates become veqr slow when the K,,, values of the dissolution medium are larger than 10.. ‘If). For the carbonate-containing apatites. however, there is a significant dissolution in the region lo‘I’ 1 K ,+,r _ > lo-“” which is in the region of physiological and therapeutic significance. The present results with the HAP powder together with HAP pellet data show that the dissolution of HAP pellets in the region 10 _ ‘I4 > I(,,, > lo*19 rest&s from an extended transient period rising from sustained deposition of Fon the surface and at intermediate depths in the ‘lesion’. Similar effects have also been observed with bovine teeth dissolution in acidic Fsolutions.